Crumbling meatballs

I made meatballs a night ahead with the intention to grill them. 1 lb lamb, 1 lb beef (coarsely ground by local butcher), 2 eggs, flour and attendant spices. They refused to stick together, and crumbled on the grill. They didn't even stick together after pulling them out of the oven where we finished them off in desperation (Chicago in near-100 degree heat). What did I do wrong?

I'm definitely not an expert at this, but I do make a lot of meatballs. I would think that there may be a few causes.
1) the meat may not have had a high enough fat content, or it may have been ground too finely.
2) no binding agent. Lots of recipes use finely ground breadcrumbs to keep the whole thing together. When I don't use breadcrumbs, I use Ricotta cheese.

Ah, breadcrumbs.....yes, that would've worked better. The meat was pretty coarsely ground, so I think it must be lack of binding agent. Sub breadcrumbs for flour, and I think we're in business. Thanks!

Since I generally cook gluten-free, I've also found that uncooked oatmeal, and/or uncooked potato buds can work well in lieu of breadcrumbs. My family actually likes the potato bud version as the best of all (as my teenager quipped "Mom, it is great because it tastes like meatloaf and mashed potatoes all at once"). Anyhow, just offering another alternative. Breadcrumbs (regular or from gluten-free bread) are a well tried and true option as well.